9146( 2) - 02/15/01 09:50 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9146 Version: 2 Check-in Date: 15-Feb-2001 09:49:13 1.Proposal Title: Cepheid Masses: Y Car ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Nancy Evans Smithsonian Institution Astrophysical Observatory CoI: Dr. Kenneth Carpenter Goddard Space Flight Center N CoI: Dr. Francesco Kienzle Geneva Observatory N ------------------------------------------------------------------------------------ 5. Abstract Quantitative understanding of classical Cepheids provides confidence in their use as primary extragalactic distance indicators, as well as in the understanding of the evolution of more massive stars and more evolved stars. HST UV spectroscopy provides a unique opportunity to contribute to the dramatic improvement in the precision of fundamental stellar parameters by determining the mass of the double mode Cepheid, Y Car, the only known double mode Cepheid in a binary, which makes it arguably the top priority Cepheid mass. In this project, the orbital velocity amplitude of the hot main sequence companion is to be measured from STIS echelle spectra and combined with the orbital velocity amplitude of the Cepheid from the ground-based orbit and the mass of the main sequence companion to provide the Cepheid mass. We have already reduced the uncertainty of the amplitude of the ground-based orbit of the Cepheid from +/- 0.8 km sec^-1 to 0.2 km sec^-1. The sensitivity of the STIS spectrograph makes possible a higher dispersion observation over a wider wavelength region than the previous GHRS medium resolution spectra. We expect the radial velocities measured from the STIS spectra to reduce the uncertainty (s.d.) in the mass of Y Car from 32 \% (in the previous GHRS result) to $<$ 5\%. ------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 2] Observations Description ------------------------ Experience with GHRS spectra of several Cepheid companions has shown that the most robust way to measure velocities of the spectra (yielding the sharpest correlation peak and the least sensitivity to data processing such as smoothing) is to cross-correlate to two spectra of the same star. This is an ideal approach for binary stars, since the full orbital velocity amplitude is measured directly by obtaining spectra at orbital velocity minimum and maximum. Using the results of the orbit of Y Car (= HD 91595) in Fig. 3, orbital velocity minimum occurs in April, 2002, with an acceptable range of observation times between March 10, 2002 and May 20, 2002 (when the companion is within 1 km sec^-1 of minimum. The comparable range of observation dates for orbital velocity maximum (much broader) is Nov. 20, 2003 to May 20, 2004 (cycle 12). Hence, we are asking for an observation in both Cycle 10 and Cycle 12, which makes this a long term program. .05truein In addition, in cycle 10, a velocity standard star (HD 72660) will also be observed. This is a carefully chosen A1 V star with a well determined constant radial velocity and a low rotation velocity (Boehm-Vitense, et al. 1997). We can use this spectrum to compare the velocity from the whole STIS region with that from the limited GHRS region. This test has important implications for the previous GHRS results of the other Cepheids, as well as for Y Car. In addition, it is important for the proposed STIS observations of Y Car. We require two observations of Y Car B at orbital velocity maximum and minimum to cross-correlate directly to provide the orbital velocity amplitude of the companion with the best accuracy. However, the absolute velocity obtained by cross-correlating the Y Car B spectrum at both orbital phases with that of HD 72660 each provides a mass. This allows us to obtain a mass immediately from the spectrum requested in the Cycle 10 and to investigate the results from the larger wavelength range before the final requested Y Car observation in a later cycle. Ultimately, this also provides a direct way to estimate the uncertainty of the mass from the pair of determinations. .05truein Because the wavelength/velocity accuracy is the most important objective of this program, the following steps will be taken in making the observations to reach this goal. .05truein o Both an acquisition and peakup will be done for maximum precision in the centering of the target. .05truein o A GO WAVECAL will be taken at the beginning and end of each orbit through the identical science aperture as the science observations. An exposure 10 times the standard wavecal time will be requested (100 sec instead of 10 sec). These deeper WAVECALS will provide more counts in the primary reference lines at this setting, the lines 1777 and 1883 Angstrom, which only contain about 12 and 5 counts/pixel, respectively, in the default 10 second exposures. In addition, the deeper exposures will enable us to utilize a larger number of lines too faint to measure in the default AUTOWAVECALS. .05truein Standard pipeline processing and AUTOWAVECAL's produce velocities from STIS echelle spectra with an accuracy of 1.3 km/sec. Using the acquisition and WAVECAL approach above, based on STIS and DATA handbooks and discussion with STIS scientists, we should reach an accuracy of 0.2 pixels or 0.26 km sec^-1, although we have conservatively used 0.5 km sec^-1 in our mass error estimates. .05truein The exposure times were set to obtain a S/N of 10 at 1800Angstrom, which has been found to produce good velocity determinations in GHRS spectra. .05truein Two further details of the observations should be noted. Although the mean magnitude of the Cepheid (V = 8.1 mag) is listed in the observation summary, the brighter Cepheid (which is variable) makes no contribution to the flux at 1800 Angstrom. It is the companion, a B9.0 V star with V = 11.9 mag which will be observed with STIS (Evans, 1992). Second, with regard to the MAMA bright limits, IUE low resolution spectra of both the Y Car system and HD 72660 exist in this wavelength region. Both stars are continuum/absorption line spectra with well known fluxes that do not violate the bright limits. Real Time Justification ----------------------- Long Term Program: The optimal observing strategy is to observe the orbital maximum and minimum velocities. Because the orbit is 2.7 years, this requires a long term program. .05truein noindent Time Critical: For the same reason, observations are planned so that the velocity will be within 1 km sec^-1 of max/min. However, the acceptable period in Cycle 10 is more than 2 months, and for cycle 12 is nearly the entire Cycle (based on an estimated start time of the cycle), so this is only a mild constraint. The observations of Y Car B will require 2 visits each, which should be as close together in time as possible. .05truein noindent Wavelength accuracy: The goal of the program is to measure the velocity of Y Car B as accurately as possible. For this reason, the observations require wavelength calibrations at the beginnning and end of each orbit that are 10 times deeper (100 sec vs 10 sec) than the default AUTOWAVECALS. None. Ground-based observations of the Cepheid orbit have already been obtained. Since it is the velocity of the companion we are measuring, the pulsation velocity of the Cepheid is not relevant, and does not need to be measured simultaneously. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD91595 STAR, COMPOSITE RA=10H 33M 10.86S +/- .5", DEC=- J2000 F-CONT(1800)=1.3+/-.2e-13 SPECTRAL TYPE, B6-B9.5 58D 29' 55.1" +/- .5" V = 8.1+/-.5 V-IV, CEPHEID B-V = .62+/-.2 E(B-V) = .08+/-0.03 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE Comments: coordinates are from the Hipparcos Output Catalog Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 -0.00066 .00368 0.0 2 HD72660 STAR RA=8H 34M 1.64S +/- .5", DEC=-2D J2000 F-CONT(1800)=2.5+/-.5e-11 9' 5.8" +/- .5" E(B-V) = 0.00+/-0.02 B-V = 0.00+/-0.02 V = 5.80+/-0.02 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE Comments: coordinates are from the Hipparcos Output Catalog Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 -.0022 .0206 0.0 9146( 2) - 02/15/01 09:50 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 10-Mar-2002 AND 20-May-2002 SEQ 1, 2 WITHIN 5 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 20 HD91595 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 HD91595 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 40 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 50 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 30 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 60 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 80 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 90 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 45 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 100 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 120 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 130 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 50 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 140 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 150 HD91595 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 160 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 170 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 35 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 180 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 200 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 210 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 45 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 220 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SEQ 1, 2 WITHIN 5 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 300 HD91595 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 310 HD91595 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 320 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 330 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 30 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 340 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 360 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 370 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 45 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 380 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 400 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 410 HD91595 STIS/N ACCUM 0.2X0.0 E230H 1763 1 50 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 420 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 7] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 500 HD72660 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 0.1 S CD ------------------------------------------------------------------------------------------------------------------------------------ 510 HD72660 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 5ND ------------------------------------------------------------------------------------------------------------------------------------ 520 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 530 HD72660 STIS/N ACCUM 0.2X0.0 E230H 1763 1 30 M UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 540 WAVE STIS/N ACCUM 0.2X0.0 E230H 1763 1 100 S END ORBIT UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 9146( 2) - 02/15/01 09:50 - [ 8] Summary Form for Proposal 9146 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25ND3 0.2X0.05ND 0.2X0.09 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 10-Mar-2002 AND 20-May-2002 SEQ 1, 2 WITHIN 5 D END ORBIT SEQ 1, 2 WITHIN 5 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230H ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD91595 WAVE HD72660 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1763 ------------------------------------------------------------------------------------------------------------------------------------